The foundation for the invention is the laser transmission welding method, which is known per se, in which two parts consisting of a plastic material are brought into contact in the region of a joint plane. Subsequently, a welding process is performed by a laser beam that melts the interfaces of the parts in the region of the joint plane, and a permanent bond of the two parts with one another is thus produced after cooling. For this purpose, it is necessary for one part to be transparent to the laser and the other part to be opaque or absorbent to the laser beam.
Depending on the application of the finished overall part, which consists at least of the two plastics parts to be welded to one another, high strength or also safety demands are placed on the final product. Therefore, it is necessary not only to execute the welding process to join together the two plastics parts, but rather to monitor quality as or after the welding process is carried out.
For ensuring quality in such a manner, DE 10 2005 000 002 A1 proposes a method of detecting thermal damage during laser transmission welding and a corresponding device for carrying out this method. Using this known method, during the laser transmission welding of plastics, the possible occurrence of burns on the beam entry side of one plastics part can be detected accompanying the process. For this purpose, the radiation originating from the burn is detected by a corresponding element (sensor), and to therefore allow discarding of a damaged part in the context of mass production of such parts.
However, this known method has the disadvantage of an elaborate and therefore complex construction, so that it is not suitable or is only suitable to a limited extent for mass production and in particular ensuring the quality of plastics parts produced by mass production.